39 research outputs found
Gerda phase II: Search for neutrinoless double beta decay
No full textThe GERDA (GERmanium Detector Array) experiment, located at the Laboratori Nazionali del Gran Sasso, is searching for neutrinoless double beta (0νββ) decay of 76 Ge. Since the end of 2015, in Phase II of the experiment, 35 kg of enriched high-purity germanium detectors are operated in liquid argon, that serves as cooling for the detectors as well as active shield against external radiation. The aim is a sensitivity on the 0νββ decay half-life larger than 10 26 yr with about 100 kg·yr exposure and a background level of about 10 −3 cts/(keV·kg·yr). An overview of the analysis of the data collected so far is presented with an emphasis on the background rejection techniques and their performance together with the half-life limit
The large enriched germanium experiment for neutrinoless double beta decay (LEGEND)
No full textThe observation of neutrinoless double-beta decay (0νββ) would show that lepton number is violated, reveal that neu-trinos are Majorana particles, and provide information on neutrino mass. A discovery-capable experiment covering the inverted ordering region, with effective Majorana neutrino masses of 15 - 50 meV, will require a tonne-scale experiment with excellent energy resolution and extremely low backgrounds, at the level of ∼0.1 count /(FWHM·t·yr) in the region of the signal. The current generation 76Ge experiments GERDA and the Majorana Demonstrator, utilizing high purity Germanium detectors with an intrinsic energy resolution of 0.12%, have achieved the lowest backgrounds by over an order of magnitude in the 0νββ signal region of all 0νββ experiments. Building on this success, the LEGEND collaboration has been formed to pursue a tonne-scale 76Ge experiment. The collaboration aims to develop a phased 0νββ experimental program with discovery potential at a half-life approaching or at 1028 years, using existing resources as appropriate to expedite physics results
An improved limit on the neutrinoless double-electron capture of <sup>36</sup>Ar with GERDA
No full textThe GERmanium Detector Array (Gerda) experiment operated enriched high-purity germanium detectors in a liquid argon cryostat, which contains 0.33% of 36Ar, a candidate isotope for the two-neutrino double-electron capture (2νECEC) and therefore for the neutrinoless double-electron capture (0νECEC). If detected, this process would give evidence of lepton number violation and the Majorana nature of neutrinos. In the radiative 0νECEC of 36Ar, a monochromatic photon is emitted with an energy of 429.88 keV, which may be detected by the Gerda germanium detectors. We searched for the 36Ar 0νECEC with Gerda data, with a total live time of 4.34 year (3.08 year accumulated during Gerda Phase II and 1.26 year during Gerda Phase I). No signal was found and a 90% CL lower limit on the half-life of this process was established T1/2 > 1.5 · 1022 year
GERDA results and the future perspectives for the neutrinoless double beta decay search using76Ge
No full textThe GERmanium Detector Array (GERDA) is a low background experiment at the Laboratori Nazionali del Gran Sasso (LNGS) of INFN designed to search for the rare neutrinoless double beta decay (0 nu beta beta) of Ge-76. In the first phase (Phase I) of the experiment, high purity germanium diodes were operated in a "bare" mode and immersed in liquid argon. The overall background level of 10(-2) cts/(keV . kg . yr) was a factor of ten better than those of its predecessors. No signal was found and a lower limit was set on the half-life for the 0 nu beta beta decay of Ge-76 T-1/2(0 nu) > 2.1 x 10(25) yr (90% CL), while the corresponding median sensitivity was 2.4 x 10(25) yr (90% CL). A second phase (Phase II) started at the end of 2015 after a major upgrade. Thanks to the increased detector mass and performance of the enriched germanium diodes and due to the introduction of liquid argon instrumentation techniques, it was possible to reduce the background down to 10(-3) cts/(keV . kg . yr). After analyzing 23.2 kg . yr of these new data no signal was seen. Combining these with the data from Phase I a stronger half-life limit of the Ge-76 0 nu beta beta decay was obtained: T-1/2(0 nu) > 8.0 x 10(25) yr (90% CL), reaching a sensitivity of 5.8 x 10(25) yr (90% CL). Phase II will continue for the collection of an exposure of 100 kg . yr. If no signal is found by then the GERDA sensitivity will have reached 1.4 x 10(26) yr for setting a 90% CL. limit. After the end of GERDA Phase II, the flagship experiment for the search of 0 nu beta beta decay of Ge-76 will be LEGEND. LEGEND experiment is foreseen to deploy up to 1-ton of Ge-76. After ten years of data taking, it will reach a sensitivity beyond 10(28) yr, and hence fully cover the inverted hierarchy region
The GERDA experiment for the search of 0νββ decay in ^{76}Ge
No full textThe Gerda collaboration is performing a search for neutrinoless double beta decay of 76Ge with the eponymous detector. The experiment has been installed and commissioned at the Laboratori Nazionali del Gran Sasso and has started operation in November 2011. The design, construction and first operational results are described, along with detailed information from the R&D phase
Search for neutrinoless double beta decay with GERDA phase II
No full textThe GERmanium Detector Array (gerda) experiment, located at the Gran Sasso underground laboratory in Italy, is one of the leading experiments for the search of 0 nu beta beta decay. In Phase II of the experiment 35.6 kg of enriched germanium detectors are operated. The application of active background rejection methods, such as a liquid argon scintillation light read-out and pulse shape discrimination of germanium detector signals, allowed to reduce the background index to the intended level of 10(-3) cts/(keV.kg.yr).
In the first five month of data taking 10.8 kg yr of exposure were accumulated. No signal has been found and together with data from Phase I a new limit for the neutrinoless double beta decay half-life of Ge-76 of 5.3 . 10(25) yr at 90% C.L. was established in June 2016. Phase II data taking is ongoing and will allow the exploration of half-lifes in the 1026 yr regime. The current status of data taking and an update on the background index are presented
Pulse shape analysis in Gerda Phase II
No full textThe GERmanium Detector Array (GERDA) collaboration searched for neutrinoless double-\beta decay in ^{76}Ge using isotopically enriched high purity germanium detectors at the Laboratori Nazionali del Gran Sasso of INFN. After Phase I (2011–2013), the experiment benefited from several upgrades, including an additional active veto based on LAr instrumentation and a significant increase of mass by point-contact germanium detectors that improved the half-life sensitivity of Phase II (2015–2019) by an order of magnitude. At the core of the background mitigation strategy, the analysis of the time profile of individual pulses provides a powerful topological discrimination of signal-like and background-like events. Data from regular ^{228}Th calibrations and physics data were both considered in the evaluation of the pulse shape discrimination performance. In this work, we describe the various methods applied to the data collected in GERDA Phase II corresponding to an exposure of 103.7 kg year. These methods suppress the background by a factor of about 5 in the region of interest around Q_{\beta \beta }= 2039 keV, while preserving (81\pm 3)% of the signal. In addition, an exhaustive list of parameters is provided which were used in the final data analysis
Search for tri-nucleon decays of Ge in GERDA
No full textWe search for tri-nucleon decays of Ge in the dataset from the
GERmanium Detector Array (GERDA) experiment. Decays that populate excited
levels of the daughter nucleus above the threshold for particle emission lead
to disintegration and are not considered. The ppp-, ppn-, and pnn-decays lead
to Cu, Zn, and Ga nuclei, respectively. These nuclei are
unstable and eventually proceed by the beta decay of Ga to Ge
(stable). We search for the Ga decay exploiting the fact that it
dominantly populates the 66.7 keV Ga state with half-life of 0.5 s. The
nnn-decays of Ge that proceed via Ge are also included in our
analysis. We find no signal candidate and place a limit on the sum of the decay
widths of the inclusive tri-nucleon decays that corresponds to a lower lifetime
limit of 1.2x10 yr (90% credible interval). This result improves
previous limits for tri-nucleon decays by one to three orders of magnitude.Comment: 8 pages, 9 figures, 3 table
Calibration of the GERDA experiment
No full textThe GERmanium Detector Array (GERDA) collaboration searched for neutrinoless double-β decay in 76Ge with an array of about 40 high-purity isotopically-enriched germanium detectors. The experimental signature of the decay is a monoenergetic signal at Qββ =2039.061(7) keV in the measured summed energy spectrum of the two emitted electrons. Both the energy reconstruction and resolution of the germanium detectors are crucial to separate a potential signal from various backgrounds, such as neutrino-accompanied double-β decays allowed by the Standard Model. The energy resolution and stability were determined and monitored as a function of time using data from regular 228Th calibrations. In this work, we describe the calibration process and associated data analysis of the full GERDA dataset, tailored to preserve the excellent resolution of the individual germanium detectors when combining data over several years
